My last blog post pondered what was needed to share objects between "platforms" (ie .NET, C, Python, C++/std, C++/Qt and so on). This time, I'll be thinking out loud about potential systems that we could use in free software land. It'll be long, humour me. I promise I won't do it again ;)

I think there are basically 3 different types that stand a chance of being accepted. I'm going to exclude CORBA from this list on the grounds that it has already have a good attempt at the market, and failed to make a noticeable impact. So:

The first type is some derivative of COM

COM has been endlessly imitated throughout the years - because its core is so simple, it's easy to duplicate. For instance, Mozilla uses XPCOM, which is a simpler, slightly cleaner variant (but is designed for internal usage only rather than operating system wide usage). From the XPLC web site, I'd guess that's similar to COM also. The basic features of a COM style system are that you pass around arrays of function pointers (an interface), and each object must expose at least one standard interface, typically similar to IUnknown (XPCOM uses nsISupports).

I don't think a COM derivative is right for us. In order to be truly useful especially for performing language bindings many things must be built on top, like for instance a variants API. Because all this must fit in the basic framework of cascaded function tables, it's difficult to get a natural API. Microsoft themselves are leaving COM behind in favour of .NET - it would be foolish to head in a direction the dominant technology provider is leaving. COM systems often require free floating external magic, for instance a registry somewhere. Getting people to agree to depend on this would probably be difficult - the "what's in it for me?" factor gets in the way. While COM would work, it'd not the best we can do. There is also no widely deployed implementation available - having working code on peoples systems is a great boon. A COM style system does have the big advantage of being a known quantity, and at least to most politically acceptable if not technically so.

The second type of system is a common language runtime

.NET provides a CLR and CTS (common type system). As far as I know, .NET is the first attempt to produce a truly generic compiled ABI - traditionally they have always been designed for a particular language.

A quick review - .NET allows language interop not through making languages "skins" of C# as some have cynically suggested, but by providing a unified binary format and type system. Managed C++ extends C++ for instance, but it's still possible to compile the entirety of Microsoft Word with it. Some people seem to think that if a language has a form that can be compiled to MSIL it must be "crippled" - in fact this is no more the case than a language being crippled because at some point it must be translated into x86 opcodes.

The "crippled" accusations normally arise because people see that in order to share objects with other .NET languages they must conform to the common type system. This much is obvious - only C++ supports multiple inheritance so an API that makes use of this feature cannot be used from a language that does not support it. That doesn't mean you can't use multiple inheritance in .NET, it just means that objects you create using it will only be usable by other Managed C++ programs.

Clearly, in order to share code you must have a common ground, this was covered in my previous posts. The .NET CTS is an extremely rich common ground, and therefore .NET APIs can be very expressive. Because the .NET class hierarchy is available to all .NET langauges that understand the CTS, it's possible to write an API in say Python that returns an XML document usable from C#, as long as they use the common ground provided by that shared class library. You're free to write and use APIs that work in terms of PyXML of course, but don't expect to be able to export that to other languages. Sharing code between platforms is always going involve a set of compromises, but this one is unusually good.

The approach .NET takes to allowing code interop is technically elegant, and makes the most sense. Creating a rich shared ABI, object model, a strong introspection framework for interpreters and also providing a shared class library is probably the ideal way to enable code sharing at the technical level.

We now hit a problem

Creating all this infrastructure takes a huge amount of effort. It's taken Microsoft years to produce .NET - so far there is no equivalent being produced by the open source community. No, Parrot is not it - even assuming they overcame the technical problems with some see with their designs, it still only provides one part of the puzzle, namely a VM and new opcode/binary format. As far as I know, Parrot does not provide a shared object model, type system, and it most certainly does not provide a shared class library. Parrot is not specified anywhere, it's magic, - by contrast, the core of .NET is specified in ISO standards.

It could be done of course, by a team sufficiently dedicated. But, what you'd end up with would simply be something very much like .NET but incompatible - where is the logic in that? It makes more sense then to clone .NET exactly, and remain compatible with Windows - something we need anyway if we are to run many of the apps of the future. For this of course we have Mono, and a very important project it is even if you really don't like .NET at all. It's the Wine of the year 2010.

Mono, of course, has understandable political problems. Remaining compatible with .NET has a tangible cost, both technically and socially. It not only causes wierd hacks and warts like using the PE format for binaries instead of the more common on Linux (and somewhat superior, imho) ELF format, but socially it places control of the shared platform in the hands of a sworn enemy of not only Linux but the entire free software movement.

It's not surprising that people question the wisdom of writing free software for Linux on this framework. Don't get me wrong - patents do not enter into my argument here - rather, I'm more concerned about the cost of having Microsoft dictate the design of the framework and the statistical difficulty of "forking" it - we need Mono to be compatible with MS.NET for the apps, so we cannot simultaneously take it in another direction if we disagree with what Microsoft are doing.

Is there are 3rd alternative?

Of course there is. It's not perfect, far from it. It's not as wide-reaching or elegant as .NET, it's not as simple or well understood as COM. It is, like all attempts to bridge different platforms, a set of compromises.

It's GObject, or rather, a derivative of it. Most people here probably see GObject as a way of bringing object orientation to C, something already done by C++ and Objective-C years ago. In fact, one of the primary motivations for developing GObject was the need for a way to make language bindings very easy to do, and at this task it succeeds admirably. Often the parts of GObject that seem unnecessarily complex such as the dual phase destruction process are there to support language bindings - in this case, dual phase destruction allows garbage collectors to break up reference counting cycles before destroying/freeing the individual objects.

GObject is not especially fun to define objects in. It typically requires a lot of boiler plate code, a lot of tedious typing and so on. This is not a valid reason for avoiding GObject in our quest to share code. The need to write lots of code to define an object is only true in C, and by its nature, everything in C is tedious and involves a lot of typing. If you want ease of use, use Python, not C.

The reason GObject is valuable for sharing objects is that it provides a rich object model, type system and more importantly it exposes it all via a C API - accessing it from C++, Python, .NET and so on is easy.

Typically today, GObjects are written in C. There is no particular reason why that must be the case, in fact there is already a proof-of-concept program that uses .NET reflection to examine a .NET object hosted by Mono and spits out libmono->GObject bindings. You can then apply the PyGTK codegen code to bind it into Python, C++ and so on.

You can of course also go direct from .NET to Python, in at least two different ways. The first is to write a Python interpreter that spits out MSIL, and that is then JITed by the mono runtime. I think ActiveState were working on something like this. Unfortunately Python is largely magic remember - there are no guarantees that code runs perfectly unchanged when we do that. The other way is to do direct Mono<->Python bindings, ie that use the libmono/libpython C apis to directly map objects between them. This is possible because both platforms support good reflection/introspection capabilities.

What advantages does using C/GObject as our "hub" bring?

The first is that GObject is a very rich object model - almost as rich as the .NET one, I think. It supports things like signals, which typically have to be bolted onto a languages native object model (see libsigc++). It supports a variety of memory management models. It supports properties, static and virtual methods (kind of, see below), and it supports arbitrary string->value associations. You can do inheritance with it, in contrast to COM which does not really know about that.

The second is that the combination of GObject, GLib and C also provides a lot of the infrastructure needed to usefully share code in the form of a common type system, variants api, marshalling infrastructure, common data types and so on, which are frequently very minimal. There's no need to haggle over the definition of a list, because it's already been defined, and has only the bare essentials. The binding logic is free to layer on top any API it sees fit - translating a GList (which is little more than struct { void *prev, *data, *next }) into a QList which provides a much richer API is straightforward.

GObject has a few practical advantages. It already exists, which is a major plus, and better, is already deployed - every Linux (and FreeBSD and Windows) system that has GTK has GObject. It's well understood - GObject has been used to bind many types of objects into other languages, not just widgets or GNOME APIs - the GNU Triangulation Library, for instance. There is documentation, experience and tools available to make the job of producing the wrapper code easy.

The final advantage of GObject is that it doesn't depend on the user to set anything up. If GTK is installed, that's all you need. There's no registry, no runtime needed - as long as you can deal with shared objects, you're sorted. It can be used entirely internally, for instance you can write parts of a program in C and parts in Python.

GObject though falls short in a few places.

For instance, an object bound into Python from C will not respect virtual method overrides - GObject/GType knows nothing about virtual methods, and there is no set convention for them. A mix of styles is currently used, with no easy way to override methods as a result. I have some ideas for how that could be made better. The defs file format which expresses an API (similar to COM/CORBA IDL) is not specified anywhere, nor even really documented it seems. The tools to bind objects from C are plentiful but the tools to bind objects to C are virtually non-existant. Thread safety is not really handled, unlike in COM where thread safety is (rightly) specified as part of the objects interface (well actually its specified in the registry, not IDL) - though arguably this should not be a part of the object system at all.

Its last problem is that its name starts with a G. Yes, this is really sad, but it causes problems for some people. Hopefully the political problems (which really only seem to affect KDE developers) associated with "another desktops library" are more easily surmounted than the problems with .NET - at any rate, an extension of GObject to deal with the problems outlined above could be called, for instance, CoreObject: maybe that would help.

So, this post is about what COM gets right, and therefore what we need to copy from it :)

I do believe that we need to copy some things from it. COM on Windows has been a great success in terms of code sharing. When the Jabber team wanted Windows clients, Peter Millard wrote JabberCOM. There were no arguments over what language to use, what dependencies it could have, or how to expose the API - it was written in Delphi (a dialect of object pascal) exposed via COM and that's how it was used. End of story. Contrast this to the stupid and childish arguments that happen in the community over trivial matters of code style and utility libraries, and you see why while the rule of a dictator may be hated and unjust, it is at least somewhat orderly.

The current scenario on Linux where libraries are written in C then bound into other languages has a few advantages, but also a few major disadvantages.

The biggest advantage is that you do tend to end up with a reasonably sane, well integrated API that follows the idioms of the platform you're using. For instance, pygtk does not require you to make calls like CreateObject("{3a36cb61-e38a-43b3-aa0d-407e7cfb2168") in order to construct a window, you can just do "import pygtk" like every other native Python library. This can be done regardless of the design of the underlying API.

It does however have many disadvantages (obviously, or I wouldn't be saying we need something better). For starters, wrapping is an manhour intensive process. The bindings have to be created, then maintained. It has to be done over and over again for each language. Worse, this software doesn't actually do anything, it is "metasoftware", that simply helps us write other software better. The more time we spend writing this metasoftware, the less time we have for software that solves end user problems.

Perhaps one of the biggest disadvantages is that while theoretically you can bind from any platform into any other, in practice all the experience and tools is in going from C to somewhere else. It's common to find bindings for a library written in C to Python, but rare (in fact I've never heard of one) going from Python into C. They are both theoretically possible, it's just that one is unexplored territory so the conventional wisdom is that if you want to share code, it must be written in C.

Clearly this attitude is not productive. C is not an especially efficient language to work in. Higher level languages can be used to get things done a lot quicker, and while Python (and maybe in the future mono) is taking off for applications the same is not true of software components.

So what do we need in order to share software components between "platforms" (which for want of a better word is the term I'll use to mean C vs C++ vs .NET vs Python and their associated standard libraries)?

The basic requirement is a shared object model. An object model tends to consist of a) a set of agreements on how things should be done and b) some sort of "magic", by which I mean opaque implementation details. COM for instance is roughly equal parts agreements and magic - COM components must use the COM reference counting model, must implement IUnknown and so on, however they don't necessarily have to rely on the CoCreateInstance() activation registry magic. While IDL is a formalized agreement, the code that turns that agreement into code you can invoke from your chosen platform is magic.

The magic to agreements ratio of object models varies wildly. The C++ object model for instance is almost entirely based on agreements, for instance between compiler vendors on the ABI to use, and as embodied in the C++ language specification. The lack of any ABI agreements on Windows was one of the driving forces behind the uptake of COM. From the users perspective a lot of this takes place automatically, but they could if they wished format the ABI themselves (to construct vtables on the fly for instance) - it's just that nobody does it, because it's so complex.

In contrast, the Python object model is almost entirely magic. There is only one canonical implementation of the Python object model, the one produced by the Python project. Alternative implementations such as found in Psyco tend to be a little buggy. The advantage of a magic based object model is that you're not tied down by standards, and you are therefore much freer to extend or improve it. Magic is also a lot easier to work with, you can rely on quirks of the magic to get things done.

In order to share objects between platforms a common ground is needed, in other words you need a shared object model. In the case of COM, this model is very simple, it can hardly even be called an object model at all. CORBA is rather more advanced but rather more complex.

Of course COM does not just provide an object model. It also provides network transparency and thread safety to its components. I'd argue that these things are actually entirely separate issues that should not be glued onto a shared object framework simply because it's sort of possible, though there may well be a separate, clearly defined way to get these features in the context of the framework. The overheads and complications that seep into COM because of the location transparency generally aren't worth it, IMHO.

We don't have very many possibilities here, unfortunately. There are at least three different shared object models that we could use in the free software community (and that have a slight chance of being accepted). Next time I'll go over what they are, and which I personally would choose.

Perhaps in future once autopackage is up and running, I might try my hand at hacking one of them up. We'll see how it goes.

So pphaneuf was wondering what was up with COM. I'm not the guy who wrote the original rant, but I've worked quite a bit with the COM/OLE subsystem of Wine lately, so perhaps I can provide some insights.

COM attempts to solve a simple problem - providing a stable, language neutral in process ABI that allows components from many providers to work together, without the source code.

Well. That's the theory. In fact, COM has been used to do all kinds of things over the years. So pretty quickly we reach the first problem with COM:

1) When all you have is a hammer, everything looks like a nail.

COM and the various technologies built upon it (which are often referred to just as COM) such as OLE/ActiveX/DCOM and so on, have been used for the following things over the years:

To allow Excel to embed itself in Word and vice-versa

To try and make the Win32 API object oriented

As a replacement for designing network protocols

As a system for IDE plugins/OCX controls (which is really just a specialisation of OLE compound documents)

As a Java-applet killer

As a way to expose code to Visual Basic. In fact OLE Automation was originally developed for the VB engine (which is why it uses BSTRs, the B stands for BASIC)

That's just off the top of my head. In all these things, a technology like COM can be used, but that doesn't mean it's actually the best technology for that particular purpose. Unfortunately, because COM is so flexible, there has traditionally been a tendancy in Redmond to try and ram a square peg into a round hole.

COM is mind bogglingly complicated. That might surprise people who know the basics - and in a way it is surprising because the core of COM is very simple. Components are black boxes, that support interfaces. Interfaces can inherit from each other, and all interfaces inherit from IUnknown, which provides the basic services every COM object must implement.

So we reach the 2nd reason COM sucks:

2) COM is not actually object oriented.

You cannot inherit any functionality from IUnknown, only a contract, so you have to reimplement the IUnknown functionality each time. Because of that, IUnknown is very simple and provides almost no functionality.

Interfaces are basically vtables, ie a table of function pointers. IUnknown provides reference counting, and the ability to query for other interfaces. That's it. In comparison, for instance, the GObject base provides methods, properties, public variables, signals, arbitrary data association, reference counting and so on. So, COM objects tend to be quite primitive.

Actually I lied earlier. You can do inheritance in COM, by using a technique called aggregation. Unfortunately this is such a pain in the ass nobody does it.

Seems simple enough so far, right? To build a COM object, all you need to do is implement IUnknown and then whatever interfaces you need. Well, almost.

3) COM sucks because it forces often unnecessary optimizations upon you

All COM objects, if they are going to be instantiated via the standard CoCreateInstance API, must have an associated class factory. Because having COM instantiate an object for you is expensive, the designers decided that actually CoCreateInstance should return a class factory - ie an object which exists only to create the actual object you want. You can then create instances of the object you want very easily, just call the right method on the IClassFactory interface.

Of course, not all objects need creation efficiency. Many are one shots, you don't need to create them thousands of times per second, you create them perhaps once in the lifetime of the app. Unfortunately, COM forces the class factory paradigm on you. And of course, you have to implement it yourself.

Well, that isn't quite true. You can get toolkits, frameworks and IDEs which automate a lot of this boilerplate for you - unfortunately we just fell into Windows syndrome where problems with the underlying framework are disguised by having an IDE write code for you, rather than fixing the problem.

4) COM sucks because it starts simple, then rapidly gets complicated.

OK, so far it's all been conceptually easy, if rather a lot of typing. But at the moment, your object is not that useful. For it to be used from other languages/environments, you need to define the interface in IDL. MS IDL is not a simple language. It's the job of the midl compiler to turn IDL into header files that describe the object, so you can easily invoke its methods.

IDL can be compiled into several different things. Header files for C/C++ is one obvious target, but you can also make "type libraries", which are binary equivalents to the IDL. Sort of. Unfortunately, even though there are two different TLB file formats (with the same extension), neither of them can completely represent everything available in IDL.

For instance, a type library cannot represent the IDispatch interface, which is a core COM interface. You need support for that built into the framework.

Type libraries can also be compiled into a DLL as a resource. At that point, you basically need an IDE to extract it, and create the boilerplate code necessary to represent the vTables in your language.

So back to IDispatch. What's that?

5) COM sucks because late binding is truly horrid

IDispatch allows you to perform "late binding" on an object. Rather than needing to know the layout of the vtable at compile time, you can pass IDispatch a string representing the method you wish to invoke, and a set of arguments. It'll then invoke that method, and return the result. It's needed if you want your COM object to be accessible from a scripting language like JScript, VBScript, or ... yes, Visual Basic itself (which internally makes heavy use of OLE Automation).

Unfortunately, IDispatch is the interface from hell. MSDN recommends that you don't attempt to implement it yourself, because you'll get it wrong. It over optimizes (again) - for instance you don't pass the method name to IDispatch::Invoke, you pass a numeric ID, which you must retrieve beforehand from IDispatch::GetIDsOfNames. Why? For speed. Unfortunately, Visual Basic doesn't actually use this optimization - it was decreed that keeping a cache of method names to member IDs was too complex and easy to screw up, so it does the lookup each time. You still have to implement it of course.

In order to make this situation suck less, Microsoft provide a few implementations of IDispatch for you. One of them, the one it's probably best to use, uses type libraries! Ah, that's better. You just have to write your IDL, compile it to a type library, and then delegate IDispatch to ... oh, wait. LoadTypeLibrary, then GetTypeInfoOfGuid, then CreateStdDispatch, but then you have even more arbitrary limitations placed on you.

Don't worry. If you're using Delphi, this is all sorted out. Just don't forget that you can only have one IDispatch per object. If you have three interfaces you'd like to expose via OLE automation, you have to choose one, or get into "dispinterfaces".

Oh yes. Finally, remember that IDispatch::Invoke works in terms of the variant API. The Win32 VARIANT is really scary. Variants can contain not just about a zillion types of numbers, but also things like BSTR, the most annoying string type in the world. Variants can also contain other dispatch interfaces.

6) COM sucks because DCOM is really complicated

DCOM lets you remote interfaces into other contexts. What is a context? COM defines an "apartment model", which typically means thread. If a COM object is STA threaded (single threaded apartment) then it's not thread safe (ie, most COM objects), so if you want to access it from another thread you must marshal the interface into that thread. Remember to run a message loop though! If you don't, DCOM will start sending window messages to that hidden window you just implicitly created, and your app will deadlock.

COM supports many different threading models, not all of which are supported by all versions of Windows. What the difference between the apartment, free, or both threading models is, is buried inside books like "Essential COM".

You can also marshal interfaces into other processes or machines of course. Of course we now come back to the thorny issue of exactly how the interfaces are marshalled. One way is to use type libraries again, but remember they can't represent everything that IDL can, so sometimes you'll have to generate marshalling code manually. I say manually, of course the RPC NDR APIs are so baroque - NdrUserMarshalMarshall() anybody? - that this isn't possible, so you have to let midl do it for you. The code MIDL generates does some extremely wierd things - look but don't touch, and don't ask questions whatever you do. The code is also messy, using a bizarre mix of indent styles.

I'm not going to continue, this entry/rant is already far too long. Just take a look through the (extensive) COM APIs some time, and note how many functions there are that appear to exist for no better reason than invoking a certain function on an interface, or creating a certain object while by passing the standard mechanisms to do so.

Next time - why COM doesn't suck, and what we can do in free software land to get the benefits of COM (which are many) while avoiding the suckyness of a system that's been grown over a period of a decade.

Congrats to the GNOME developer team on 2.4, I'm looking forward to playing with it when the next Red Hat is out.

Wine wise, things are good. WineCfg continues to make good progress, mini-flamewars over instant apply on the side. Some highly dubious statistics were thrown around, for instance "70% of linux users use KDE, 90% of people use Windows, so therefore 99% of people are not used to instant apply".

Personally, having used both types quite a bit, I find instant apply to be much nicer, it actually makes the machine feel faster (or does to me), and I didn't have any problems adapting to it. On the other hand, I didn't have any problems with the Gnome2 button ordering either, and I know some people found both these things very disruptive (well, a few did, because they bitched about it online).

Now, there are arguments for doing both things in winecfg. Most seem to agree that on its own, instant apply makes sense, and has good usability. The arguments for the old way basically boil down to "That's what the rest of the world does!" which at least in my view is a rather weak argument. Nonetheless, conformance does have some merits.

The difficulty seems to be a belief that consistancy with Windows and KDE is a good thing. KDE tends to be consistant mostly with itself and Windows, not necessarily any particular set of usability guidelines, so I'm not inclined to use that as an example. Likewise, despite being implemented using Win32, winecfg will be used exclusively by users of the Linux desktop (well also freebsd etc as well). At that point it boils down to consistancy with either KDE or GNOME, and given the usability arguments each side can present, I'd favour the same route chosen by Gnome.

Hence - we have an instant apply winecfg.

Can I be bothered with the flamewars and controversy though? Probably not. It's a very little thing. Worse, Win32 does not have good support for instant-apply dialogs, the PropertySheet API we're using for instance does not support it. The transactions system I did internally can support both easily enough. Possibly a command line switch might be used, so the Gnome menu launches "instant apply mode", and the KDE menu launches "OK/Cancel" mode. You could use the OnlyShowIn property of the .desktop format to control this.

I can't help feeling that it would be ultimately a bad idea. User interfaces are more malleable than APIs, and while Wine is a fairly conservative project, in this respect I think it should be more flexible. Alexandre appears to have little opinion on the matter, he generally indicated he wanted instant apply in the future but has not yet weighed in on the debate.

On the other hand, it's not all been argument - I might be getting a contract from Relux Informatik AG to port their software using Wine, as they are interested in a Linux version of their software. Being a specialist lighting design app though, there is not a chance of a full port, it would basically mean a rewrite which is clearly not acceptable. Is this the start of my own little company? I hope so :)

So the project is growing. Lots and lots of nice comments on OSNews about the 0.3 release, which is really great. It's cool that people are so enthusiastic about the work we're doing.

The next release, 0.3.5, is time based. That's not because we're moving to time based releases, it's because in October I go to Durham university, so it'd be nice to kick out another release before then. It's mostly focussed on bugfixes and stability improvements (well, we so far do not crash, but by stability I mean working well on all distros).

There's still a long way to go, but at least the path is clear.

Wine

winecfg continues to make good progress. A lot of the work has involved cleaning up the codebase (which was a bit yucky, imho, hungarian notation all over the place, a wierd mix of styles etc), and rearchitecting it to be transactional. That means we can do instant apply Gnome2 style, which Alexandre seems to like. Unfortunately Win32 does not have great support for this style of config dialog, so we might have to add a few Wine extensions.

While we're at it, we're cleaning out some crack prefs. When even the developers don't seem to know what a preference does, it's time to worry :)

The most frustrating thing about Wine is that everywhere I turn, I find new things I want to do. Theming, making all my apps work, fixing InstallShield, merging DCOM, winecfg, better standards compliance, better desktop integration! I want to do it ALL but don't have enough time or energy (of course).

I've had pretty good productivity lately. In fact, I currently have 8 outstanding patches against Wine that haven't been committed yet. Alexandre has been busy with rearranging the 16/32 bit code, amongst other things, and commits from external contributors have slowed down a lot. I find myself wondering, not for the first time, if Wine would not proceed quicker with more committers. OTOH the Q&A Alexandre provides is certainly a benefit, especially for people like me who aren't hugely experienced with Win32, nor writing thread safe, OOM-safe code in C.

I've been mostly hacking on winecfg - the Wine projects official configuration GUI. The eventual plan is to scrap the config file, and move it all into the registry. In fact, this is a goal for the 0.9 "easy to use" release of Wine. Win32 isn't the easiest toolkit to work with, and it becomes doubly harder when you don't have an IDE to write the gobs of template code it needs. As a result, progress is not as fast as I'd like. Still, the end result should be good.

I started looking at MSN Messenger last night. If worst comes to worst, and Gaim and Jabber are forced off the network (I doubt that'll happen), then we might have a backup plan in being able to run MSN Messenger itself. Another interesting possibility is a build of Gaim that is a WineLib app and uses the MSN ActiveX control directly. More likely however, is that the Gaim team come to an agreement with Microsoft, or the plugin becomes "contraband" software like the DeCSS and MP3 plugins - we'll just shove it into the freeworld repos.

autopackage

We're getting ready for the 0.3 release of autopackage. This is the first release to feature a GUI, and though it's still incomplete I'm pretty pleased with how polished it's feeling. We've put a lot of work into thinking through how users are going to interact with software installation on Linux in the future - the long term goal is that packages can be dragged out of the webpage, direct onto your panel and all the complex machinery of package management takes place behind the users back, entirely automatically.

We hope that if we do some day build such a system, it'll be generic, ie not tied to autopackage.

Some of the spit-n-polish work we put into the autopackage GTK front end will make its way back to GTK eventually. For instance, we have developed a few patches for EggStatusIcon. Whereas before it blinked harshly on and off, it now gently pulses. Small details make big differences. Expect more such transition-animation work in the near future.

We've also got code now that will automatically download the autopackage support code and GUI if they aren't present on the users system. This works surprisingly well, and is now the preferred way for people to install autopackage (unless they are a developer). Our download times are currently satisfactory - about 8 seconds on dialup for the core code, and about 15 seconds for the GTK gui, meaning a total of about 20-25 seconds delay for dialup users. For ADSL/cable users, it's probably nearly instant. Those times will go up as we add more code, which might start getting problematic - it could be worth learning about optimizing code for space, though I doubt there's much we can do that will make a big difference.

That code was written not by me, but by Hongli and Curtis. I haven't said this before, but I feel I should - they are consistantly smart, helpful, reliable contributors who produce work of the highest quality. They're the sort of contributor every project maintainer wants about a hundred of, and I'm very lucky to have two. Still - the task is pretty big, even for three of us working on it as our primary projects. Our last release was on the 12th July.

bgeiger: I suspect if you have an even slightly modern x86 based PC and actually performed some speed tests, you'd find that the fact that a Mac feels fast doesn't mean it is fast.

Now feeling fast is a mighty spiffy trick, and mostly boils down to the way they double buffer the windows and use VSYNC to good effect.

To be honest, I've used MacOS X and wasn't impressed. It's great demoware, and a good OS, but nothing we can't beat the living snot out of in free software land given a bit of work. Anyway, unless you will enjoy writing Yet-Another-Cocoa-Instant-Messenger, there's not much to do there except wait and see what Apple does next. Hardly thrilling stuff.

Inspired by the ever interesting Chris Brumme, who blogs for Microsoft on .NET and Windows technical matters, I thought I'd steer this blog more towards technical writings on autopackage and Wine.

Though I do have a personal journal elsewhere, I haven't posted to it for a while, partly because now I'm back at home I'm just a phone call away from all my friends, so we have less need of it to keep in touch, and partly because since my hostelling trip around Europe ended unhappily for various reasons, not much is happening around here.

If you enjoy these mini-articles then please let me know, and if there's something you'd like me to write about, ditto.

Wine and InstallShield

One of the problems that has plagued Wine for a very long time now is (perceived) unreliability. Many people fail to get Wine working with their favourite apps, or even any apps at all. Part of the problem is that we recommend you use a fake windows drive, then install your applications into it, though as far as I know this recommendation is actually buried deep in the users guide.

The reasons for that are pretty simple - typically Windows installations have huge piles of rubbish that get in the way and can confuse Wine, not to mention that it stresses components that generally don't get much testing, like the code which reads and writes to the binary registry format. In the age of NTFS filing systems, the lack of writeability can likewise cause difficulties.

Unfortunately many people fall at the first hurdle, namely installing apps. Thanks to the near total lack of package management on Windows, there is a glut of installers all of which have different behaviour, and many of which are very complex under the hood. InstallShield falls into this category, and is a program that has given Wine problems for many years now. The difficulties with InstallShield basically fall into two areas:

1) Window management
2) DCOM

Window management has long been an achilles heel of Wine, as Win32 window management is close enough to X11 to make a mapping worthwhile and valuable, but different enough to cause serious problems in certain scenarios. The main difficulty lies in the location of the window management code.

In Windows, the application is responsible for performing its own management, or to be accurate it delegates via the default window procedure (message handling code) to libraries provided by Windows. Those libraries draw the window decorations, provide the default move/resize behaviour and so on. That simplifies the architecture somewhat, and means that opaque resizes don't suffer as much from loss of sync between the border and the contents (a problem which Havoc Pennington has been writing a patch for in metacity) but also means that if the app freezes, the window becomes impossible to move, minimize or close. In fact in XP the kernel has a hack for this, such that if a window stops responding it's silently replaced with a faked OS level window so you can still move it and resize it.

In contrast, on X11 based systems like Linux, the window management is performed on behalf of the application by a WM, a dedicated application. This program draws the borders for the app, controls its position, which buttons are available and many other things.

Typically, this distinction does not cause problems, but some apps take advantage of the implementation details. WinAmp for instance, actually creates a standard window then overdraws its own window borders with the skinned versions. Clearly this isn't possible in X11 so for times like this Wine has an "unmanaged mode", where the window is disconnected from the WM and Wine performs all its own management, which is closer to how Windows itself operates.

Unfortunately, that approach has several problems as well. For starters, the windows don't respect the virtual desktop you're on, nor z-ordering. This means that unmanaged Wine windows seem to be "nailed" to the screen, often making the app unusable in the real world.

The problems with InstallShield arise from the fact that typically, for reasons of intense LSD tripping on behalf of the developers, these installers take over your screen with a nice big blue background. Unfortunately, Wine cannot currently make managed full screen windows, as the protocols for that have only recently been agreed upon, so it defaults back to unmanaged mode. We now have a problem - with no real window management in use, the actual installer windows it opens on top of the blue background will appear underneath the background window, and worse there is no way to raise it to the top.

Because of this, for some time Wine has shipped in its default config file AppDefault entries which force all known installshield executables (they have seemingly random names) into "desktop mode". This, in theory, creates a window which contains the virtual Wine desktop, and means that Wine can accurately control and render the Windows without X interfering. Unfortunately for architectural reasons, desktop mode doesn't operate as you might think - each window gets its own desktop.

Until recently this wasn't a problem, but a bugfix elsewhere in the x11 driver now causes Wine to die with an X11 Client error when it attempts to shift multiple windows in desktop mode around. This problem renders InstallShield effectively unrunnable. There are two possible solutions to this problem - to fix desktop mode so all windows appear in the same desktop (which is what you'd expect), and to implement "half managed" mode, which is where the WM controls the window, but Wine is responsible for its position and border rendering. XMMS does something like this, and it works OK. Eventually both approaches will need to be implemented.

This leads to the second problem with InstallShield, namely its extensive usage of DCOM and RPC. DCOM, or the "Distributed Component Object Model", is the rough analogue of CORBA on Microsoft systems. It's been around for a very long time now, and is used by many apps that you would never even suspect. If you've seen a Windows 2000/XP box that's been hit by Blaster, you'll know how vital it is that RPC and DCOM are functioning correctly at all times, even seemingly unrelated things like copy and paste rely on it. That's why XP will reboot in 30 seconds if the RPC daemon terminates.

InstallShield uses DCOM primarily for inter-thread communication. While CORBA is intended for out of process communications, distributed across networks, DCOM is intended also for invoking object methods within a process. The process is fairly simple - you create a COM object that has interfaces, then marshal one of those interfaces into a stream (or alternatively, the global interface table, an object I partially implemented in Wine a few months ago). You then pass that stream to another thread, which unmarshals it. Behind the scenes, DCOM constructs a proxy/stub pair that switch the method call into the first thread context.

Exactly how it does that is a topic for another journal entry, but until recently Wine did not implement this technology. That caused InstallShield to have problems, especially with correctly redrawing its windows, although enough of the OLE/COM architecture was present to enable it to basically work. TransGaming developed a patch for WineX which implemented this part of DCOM, and thanks to the votes of its subscribers this work is now available to WineHQ. Part of my work that I talked about in my first journal entries was merging this work into the (significantly different to winex) WineHQ tree. That merge still isn't complete, but hopefully I'll get it done before going to uni in October.

At that point, the final missing piece of the DCOM puzzle will be the ability to generate binary TLB files using Wines IDL compiler, as Alexandre deemed it unacceptable to take Microsofts version (a large binary file) and stick it into CVS. Wine will then have enough infrastructure to deal with even complex usage of DCOM and OLE.

That's important because many programs use it behind the scenes, not just InstallShield. For instance, I worked on an app that embedded Internet Explorer in Java, then programmed it from another thread. That involves cross-language, cross-apartment method invocations: not a trivial thing to do, as it involves late-bound method calls via IDispatch (where you pass the numeric ID of the method and a variant array of parameters to the IDispatch::Invoke method). Sounds simple, in practice IDispatch is so hard to implement that Microsoft strongly discourage you from trying, you're told to rely on the implementations they provide instead.

Until the work is complete however, you can continue to install Microsofts OLE implementation by running the DCOM98 executable with a recent version of Wine. Make sure your config file is up to date. Fortunately this approach works reasonably well, although as the DCOM updates could be pulled at any time, and cannot be redistributed, it's important that Wine gets its own implementation. You need to run apps like this:

The first week of my holidays have been pretty hectic as I try and get everything together for travelling around Europe for a month with Ken (an old school friend of mine). I leave on Monday, should be good fun! I've travelled before, but not for such a long time.

Geek

The server (theoretic.com) that I share with a friend has started acting up again. Apache eats all the memory, and I don't know why. Originally I thought it was mod_perl, so I removed that, and it seemed to fix it, but a few days ago it died again (linux sucks at dealing with apps that eat all the memory).

I'm going to try and move autopackage to sunsite.dk, which has proper hosting. I applied earlier, we'll see what the results are. Doesn't solve my own problem though :(

Code

autopackage has been bobbing along nicely, lots of arguments between me and Hongli about the GUI design of the gtk installer frontend. There's still a lot of work to do, but I think the end result is going to be nice.

One problem we have is the lack of a decent animation format. MNG is too heavy, and doesn't fit into the gdk-pixbuf API well (it's more akin to flash than gif). I've been toying with the idea of hacking up a super simple APNG format or something that maybe could get better adoption. I might get time after I get back from Europe.

OTOH I also have a metric ton of other things to do, like trying to reduce my differential against WineHQ CVS to something sane again, doing some of the boring under-the-covers work on autopackage and so on. So, like most things, it will probably suffer from not floating to the top of the TODO list for a while.

My (ex)boss just emailed me, and wanted to know why the app I ported using Wine won't open the apps associated with a given file from Internet Explorer. Theoretically adding code to do this is not so hard, the main problem of course is the lack of a solid freedesktop standard for it. There's one in the works, but who knows how quickly it will be deployed.

That's what I call it when you finish your project at work 2 hours before you're meant to leave. Fortunately, at the end it seemed stable, though not quite as fast as I'd like.

So - I did it. I won. I didn't think I would, and I almost didn't, but I'm getting fast enough at debugging crashes, deadlocks and other nasty bugbears in Wine that I wasn't thrown when at the last minute I raised the fd limit and found it crashed in yet another way :)

Hopefully I'll be able to do a patch dump next week, so others can benefit from my work even if I don't get a chance to merge it in properly.

Life

Tonight I have to pack - I leave for home tomorrow. I've been putting it off for a while, and now it's 7pm and I've still not started. As you can tell, I'm still putting it off.

Play

Funny how work and play interlocked towards the end. I tried out apbuild today, which is a program that lets you compile the source in such a way that it will run on older glibcs. It's still rather untested, but can do Xlib and Wine (with a bit of encouragement, Wine is hard due to the games it plays with pthreads).

Of course, just after I imported it to CVS (very raw), Hongli discovers an obscure option to ld intended for platforms like BeOS that would let us get around the problems with using the LSB stub libs! ARGH! Well I need to evaluate them to see which is best, now.

We have GUIs for autopackage! Very pretty they are too, one of the nicer installer UIs I've seen for a while. Hongli (foobarwidget) is a really great coder :) There are screenshots in my home directory if you're interested, but I can't be bothered linking right now, as it's all changing so fast. I reckon people will be impressed when we do the next release though.